Loud speaking apparatus



c. c. BRADBURY 1,814,119

LOUD SPEAKING APPARATUS Filed Sept. 5, 1929 Patented July 14, 193,71

g1,814,11fa

CLIFFORD C. BRADBURY, OF GLENCOE, ILLINOIS LOUDY SPEAKING APPARATUS a ourrentin the telephone current coil tend-v in' e to movevthis coil in Vone direction-or the o er, depending uponfthe direction yof the Il induced currentl and thereby produce ai movement of theV coner ofthe speaker in accordance with thegvariations of the flux resulting in a` noise inthe speaker. An object of theinvention is to a new and improved loud speaker. f 'A 'further object is to provide a loud Speaker in which thep'force applied to the cone by the inducedcurrentl in the telephone coil-is `balanced bythe current in asimilar 'I coil associated with'a telephone current coil. A'furtherobject is to provide a device for eliminating the hum in a loud speaker mused by the flux "variations .in` the loudl speaker.

' vi( A further object is to providev a device in a loud speaker which will eifectively4 balance the effect of induced current in the telephone coil." e v A further object is to provide a loud e* speaker energized by current Vhaving a pul-V satingcomponent in Whichthe noises due to" the pulsating component are eliminated.

Oth'erobjects andadvantages will appear as the description proceeds."

di In accordance with the general features of the invention, a'movable telephone cur# rent'coil carried by the cone or diaphragm of a dynamic type loud speakerextends into the' air ga of amagnetic circuit energized iii by a recti ed current." A neutralizing coil is also carried by the cone orfdiaphragm which is mounted inf juxtaposition' to the tele hone currentcoil and is placed in 'series witlix)A a" generating ooi] associated with the W Same `nmgneticcircuit, for 'producing acure produce Application led September 3, 1929. 'Serial No. 389,903.

rent in the neutralizing coil to counteract the effect of induced currents in ytlietelephone coil. Y Y

Referring to the drawings: e Fig. 1 is a rear elevation of a loud speaker embodying lmy invention andshpwing `a ktransformer and rectifier kassociated there! with; Y Y

Fig.l 2 is an enlarged side elevation, partly in section, of the speaker -With'ts base re`` moved; e' "W -Fig 3 is an enlarged fragmentary, sectional view of the magnetic .air gapb andthe movable coils mounted therein; and

Fig. 4 is adiagrammatic'view of the telephone current and neutralizing circuits; -The apparatus comprises, in general, a base 1l having a support 12 upon which the", loud speaker 13 isl mounted, a 'step-down transformer 14 and an electronic rectlfier'l'. The magnetic circuit comprises 4a cup# shaped member 16 having a central pole piece 17 mounted concentricallyf therein and an annular pole piece 18 havinga central aperture forming an air gap 19 with the centralv pole piece 17. A field coil 22 is wound uponV the central pole piece and lcontained with-I v in the cylindrical housing formed by' the*l cup-shaped member 16 and pole piece 18; The fieldl coil 'is energized from the rectifier 15 which is supplied with valternatir'ig c1`1rrent by the transformer 14, the latter being adapted to be connected to any suitabl'ef source of alternating current supply. v

A cone l23 having'a flat peripheral mar in 25 is supported at its Vbase between annu ary rims 24. The inner rim is provided with-a plurality of, arms 26 which converge tow-ard the cylindrical housing. Theends 27 of the arms are provided with longitudinalslots 28 and are held against the cylindrical housingbyscre'ws 29 which retain Ufshaped washers 32 over the ends of the arms` to clamp the arms upon the housing.V

The apex of cone 23 has a cylinder 33 mounted thereonwhich extends into air gap 19 of thev magnetic circuit. f' Cylinder V38 is held concentric'allyin vthe ai'r'gafpby af spider 34? secured to pole l piecel 1,8 b Screws 315 and spaced 'h'erefroabr @ses This cylinder is adapted to carry a telephone current coil 37 which is conductively connected to the secondary of a transformer 40 energized by a receiving set of any suitable type (not shown).

A. neutralizing Winding 38 is also carried by cylinder 33 and is mounted upon the portion of the cylinder extending into the air gap. Neutralizing coil 3S is connected in series with a generating coil 39 Wound upon the end of central pole pieces 17 i The ends of all of the coils, as Well as oic the secondary of the transformer 40, may be brought down and interconnected upon a terminal block tl for convenience in assembling the apparatus. p

rlChe operation of the apparatus is as tolloivs: Y

Transformer la is connected in any suitable manner to an alternating current supply, energizing iield coil 22 With a uni-directional pulsating current from the rectii'ier 15. The Wave form orn the magnetic flux in the magnetic circuit will correspond to the Wave form of the current so that a ilux oi' varying magnitude will exist in the air gap into which the telephone curi-ent coil 57 extends. The varying magnetic iuX in this air gap induces a current in coil 37. The in duced current in tais coil in conjunction With the magnetic flux Will produce a movement ofthe cone and result in a noise in the speaker. In order to overcome this objectionable feature, the coil 38 which may be co-extensive and have the same number of turns as coil 37 is provided upon the cylinder and is connected to a generating coil S9 in the saine magnetic circuit.

he coil 30 should have a larger number of turns than the Winding 38 so that when these windings are connected differentially the larger number ot' turns in Winding 3f) will cause a current to flow in coil 38 which is opposite iii direction to the induced current in coil 37. The number of turns in coil 89 are so chosen as to produce a current in coil 38 Which is opposite and equal to the induced current in coil 37. Thus when a current is-lowiiig in coil 37 and an equal opposite current is flowing in coil 3S the ilus in the air gap Will have no tendency to move the cone since the torce applied to one oi" the windings is counteracted by the force applied to the other Winding With the result that the varying magnetic flux will have no effect in moving the cone due to induced currents in the telephone current coil and, therefore, no noise due to this tact will result. v 4

,It is not essential that coil 38 should have the same number of turns as coil 37-all that is necessary is that the ampere turns of these Ycoils should be equal so that if coil 38 is provided with a smaller number of turns than coil 37 a larger current Will have to be applied thereto.

The apparatus of the invention provides a convenient means for energizing a dynamic type of loud speaker and at the same time eliminates the objectionable hum found in speakers in Which the eect of induced currents from the varying rectified current is not compensated for.

Having described the nature and embodiments of my invention, what I claim is new and desire to secure by United States Letters Patent is as follows:

l. In a loud speaking apparatus, a magnetic circuit providing an air gap, a telephone current coil extending into the air gap and movable therein,l a neutralizing coil movable With the telephone current coil and extending into the air gap, and a generating coil conductively connected to the neutralizing coil to neutralize the effect of induced currents in the telephone current coil.

2. In a loud speaking apparatus, a magnetic circuit having an airgap, a sound producing member, a telephone current coil carried by said member andextending into the air gap, a neutralizing coil carried -by said member in close proximity to the telephone current coil, and a coil associated with the magnetic circuit for `generating a current for the neutralizing coil equal and opposite to the induced current'in the telephone coil resulting from flux variations in the mag netic circuit.

3. In a loud speaking apparatus, a mag-A netic circuit, means for energizing the magnetic circuit, a sound producing member, a telephone current coil carried by the sound producing member, a neutralizing coil carried by the sound producing member,and a generating coil having a larger number of turns than the neutralizing coil and associated with the magnetic circuit for generate ing a current for Ythe neutralizing coil.

4. In a loud speaking apparatus, a magnetic circuit comprising a cup-shaped member, a central pole piece mounted therein, an

annular pole piece secured to the cup-shapedr member and forming an air gap with the central pole piece, a cone for reproducing sounds, a telephone current coil carried thereby and extending into the air gap, a neutralizing coil extending into the air gap, and a generatingcoil Wound upon the central pole piece for generating a neutralizing current for the neutralizing coil.

5. In a loud speaking apparatus, a magnetic circuit providing -an air gap, a telephone current coil extending into the air gap, a neutralizing coil extending into the air gap and mechanically coupled to the telephone current coil, a generating coil in series with the neutralizing coil connected thereto in suoli a direction that the current generated inV the generating coil and flowing A` throughV the neutralizing coil is opposite in directionv to induced currents in the telephone current coil caused by flux variations.

6. In a loud speaking apparatus, a magnetic circuit having an air gap, a ield coil for energizing said circuit, an alternating current rectifier for energizing the lield coil,

a. cone for reproducing sounds, a cylinder carried by said cone having `a portion extending into the air gap, a telephonel current coil carried by the cylinder and extending into the air gap, a transformer adapted to be connected to a receiving set, the secondary of said transformer' being connected in series with the telephone current coil, a neutralizing coil co-extensive with the telephone current coil and havingan equal numberof A turns, a generating coil Wound upon the thereto, said central pole piece and having a llarger nurnber of turns than the neutralizing coil and means for interconnecting the neutralizing coil and the generating coil whereby a current is caused to flow in the neutralizing coil which is equal and opposite to the curi rent induced inthe telephone current coil.

7. In a loud speaking apparatus, a magnetic circuit, means for supplying an energizing current therefor, ymeans for eliminatlng the effect ofvariations of the energizing current comprising a neutralizing coil, and a. generating coil differentially connected generating coil having a larger number of turns than the neutralizing coil. 8. In a loud speaking apparatus, a magnetic circuit, means for energizing the magnetic circuit, a sound producing member, a

telephone current coil carried by the sound producing member, aneutralizin coil carried by the sound producing mem generating coil vdiiferentially connected in Vseries with the neutralizing coil and more subject to variation `of the magnetic circuit las 4than the neutralizing coil and associated .with the magnetic circuit for generating a current for the neutralizing coil.

s 9. In a loud speaking apparatus, a magnetic circuit, means for supplying an energizing current therefor, means for eliminating the elect 0f variations vof the energizing current comprising a neutralizing coil, and a generating coil differentially connected thereto, said generating coil being more subject to neutralizing coil.

In witness whereof, I hereunto subscribe my name this 30th day of August, 1929. l

' CLIFFORD C. BRADBURY.

er, and a Y change of magnetic circuit than the i 

